Record‐level, exceptionally broadband borophene‐based absorber with near‐perfect absorption: design and comparison with a graphene‐based counterpart

We present a high performance ultra-broadband optical absorber based on a metal-insulator-metal (MIM) configuration, enhanced by two-dimensional (2D) materials: graphene and borophene. The base design includes a titanium resonator, an SiO₂ dielectric spacer, and a gold ground plane. Performance optimization is achieved through integration of 2D materials, anti-reflection coatings (ARC), and tuning of structural parameters, Fermi energy, and surface carrier density. Numerical simulations using the finite difference time domain (FDTD) method show that incorporating borophene, due to its exceptionally high carrier density, leads to remarkable enhancement in both absorption amplitude and spectral bandwidth. When integrated with an optimized antireflection coating (ARC), the borophene-based absorber achieves over 90 % absorption across 790-3,232 nm (bandwidth: 2,442 nm), corresponding to a 136 % enhancement over the base design. For absorption above 80 %, the bandwidth extends from 760 to 3,306 nm (2,546 nm), yielding a 125 % improvement. The associated fractional bandwidths are 121 % and 125 %, respectively. By comparison, the graphene-based counterpart, with a properly tuned ARC and Fermi level, delivers over 90 % absorption within 923-2,108 nm (1,185 nm, 13 % improvement), while maintaining absorption above 80 % across 911-2,256 nm (1,345 nm, 12 % improvement), with corresponding fractional bandwidths of 78 % and 84 %. Comparative analysis underscores the critical importance of 2D material selection and placement, ARC and resonator optimization, and optical tuning in achieving optimal performance. These results indicate strong potential for practical applications in advanced optoelectronic and photonic devices, including infrared imaging, optical sensing, broadband photodetectors, solar energy harvesting, and stealth or thermal camouflage systems.